Their tentacles armed with suction cups are mainly used to help them attach
their prey.

ROB PALMER

In contrast to scuba diving apparatus, the closed circuit oxygen rebreather
provides a less wasteful means of self-contained movement underwater. This particular
set was produced by the Divers’ Equipment Supply Company, based in Milwaukee,
Wisconsin, USA during the 1940s.

In its simplest form a rebreather consists of an oxygen supply with an adjustable
flow, a carbon dioxide absorbing canister containing an alkali such as soda
lime and a reservoir or counter lung.

The diver breathes back and forth to the counter lung, each breath passing
through the absorbent, which removes the carbon dioxide. Fresh oxygen replenishes
the lost volume. The system needs pure oxygen, and is thus restricted to 10
metres. However little gas is wasted and a long duration may be achieved.

This type of apparatus was manufactured in Germany by Draeger, in Britain by
Siebe Gorman, in Italy by Cressi-sub and by others in the USA during the war
years of the 1940s.

REBREATHER STORY: HANS HASS - ROB PALMER

1942

Apart from this military use, sports and scientific divers, such as Hans Hass,
took up the apparatus. In addition, early British cave divers used the equipment
at sites such as Wookey Hole. However, there were problems.

In the trade such equipment came to be known, rather unaffectionately, as ‘One
breath from death’. The two advantages of the closed circuit rebreather system
are that no bubbles are produced and a greater underwater endurance may be achieved.
However, the disadvantages can be severe:-

Menschen unter Haien (Men Amongst Sharks)
HANS HASS, 1942

If a diver should proceed deeper than the current recommended limit of 6m,
then a pressure will soon be reached at which the oxygen, vital for supporting
biological life, becomes an absolute poison. Once the limit has been exceeded
a fit and subsequent drowning are the likely consequences. Hans Hass demonstrates
this problem, from which he was fortunately able to survive.

REBREATHER STORY: JOHN PENNEKAMP REEF - ROB PALMER

There is also the danger of producing a caustic soda mouthwash once saltwater
mixed with the soda lime. This substance is generally preferred for cleaning
the bath, rather than teeth and lungs!

Finally there is a need to purge unwanted nitrogen from the system. Air contains
20% oxygen and 80% nitrogen, all of which must be replaced in the breathing
bag and lungs by oxygen for the apparatus to work safely. The system is purged
of nitrogen by taking the contents of the breathing bag in through the mouth
and out through the nose, three times. Failure to carry out this operation properly
can result in anoxia and death.

MILITARY REBREATHER: CDBA - ROB PALMER

c.1975

In order to extend the depth capability of this type of equipment a semi-closed
circuit mixed gas rebreather was developed. Here we see a postwar military clearance
breathing apparatus, the C.D.B.A. The gas used is an elevated percentage of
oxygen in air - nitrox - with mixes between: 60% oxygen, 40% nitrogen, for up
to 20m depth, and 32½% oxygen, 67½% nitrogen, for depths of up to 50m.

The mixture is chosen for achieving a target depth, whilst reducing the nitrogen
in the body and thereby decompression time.

This mechanical apparatus relies on a ‘flow orifice’ to regulate the rate of
delivery of the mixed gas. The excess gas is dispersed from the breathing bag
via a sort of spring loaded pepper pot. This disperses the bubbles into a fine
mist, thus retaining some covert military advantage.